----- Original Message ----- From: "Robert Bonfiglio" <bon@xxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Monday, January 16, 2006 5:03 PM
Subject: [Harp-L] Tuning reeds down
An optimum reed set up might look very weird in its varying lengths and sizes, but nobody looks inside the harmonica when you play it. 25 years ago the guy at Hohner told me we would need a third World War to get the factory to change making reeds in a uniform size going from big to small on the way up the harmonica. I pointed out that the C# in hole 4 is longer than the C in hole 5 and he said that was his point, the reeds get shorter as you go up the harmonica regardless of pitch.
I agree that there is probbly an optimum length for every pitch and they would not increase linearly from one end of the harp to the other.
It is hard to fault the old timers who did a pretty good job of cut-and-try reed design. We have been using them for many years now with some success.
That said, new tools are available that should improve the design process. Finite Element Analysis (FEA) should be able to analyze a reed geometry and predict the pitch, stiffness, and stress distribution.
Stiffness relates to responsiveness and loudness. (one suspects that Hering reeds are not quite as stiff as Hohner reeds making them more responsive and a little less loud. Stiffness is determined by length and reed thickness profile.
Pitch is directly proportional to the square root of the mass near the tip and inversely proportional to the stiffness.
Stress distribution relates to fatigue. There must be stress in every reed to create the restoring force when it is deflected by the air. However, an optimum design would make the curve of stress vs distance from the rivet very smooth without any peaks or valleys and constant over a good part of the length. This is frequently disrupted by inept tuning down.
Since FEA would make it possible to quickly vary the reed geometry and then test it on the computer, optimum designs could be obtained. Unfortunately, the software to run FEA is still fairly expensive.
I also believe that stainless steel would make a better reed material than brass or bronze because it is more resistant to fatigue. If the stiffness and pitch of two reeds are the same, they sound the same even if made of different materials. I have a SS reed in a 270 that no one has been able to find by playing or listening to the harp. Unfortunately SS is very tough and the wear of the cutting tools raises its cost far above that of softer copper alloys.
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